Patent GB-1403629-A (GB)
Title: Variable speed printer
IPC: G06F3/12
Filed: 1973-02-26
Abstract: 1403629 Control of printers COMPUTER TRANSCEIVER SYSTEMS Inc 26 Feb 1973 [3 March 1972] 9397/73 Heading G4H A printer comprises means 40 for varying the printing rate in dependence on the number of incoming data bytes DS1-7 stored in a buffer 14. The bytes are stored on a first-in, first-out basis in buffer 14, Fig. 2 (not shown), from which they are transmitted byte by byte to a decoder 16 and a 1-byte buffer 18. Those bytes representing printable characters are transmitted in turn via buffer 18, gates 20, 1-byte buffer 22 and gates 24 to a dot generator 26, Fig. 3 (not shown) which provides a signal P1-P35 to activate a 5 Î 7 matrix of driving solenoids in a printhead 28 stepped across the paper by a six-step motor 36. Initially, flip-flops 50, 52 (outputs F20, F21 and F10, F11) are reset so that gates 54, 56 (and hence 20, 24) are blocked. F20 causes the first byte to be read from 14: if this is printable, a signal PG sets 50, whereupon F21 opens 54 and 20. The byte in 18 is transferred to 22 and 50, 52 are respectively reset and set: F20 allows a second byte to be read, and F11 causes control 40 to send a stepping command (a positive and negative voltage combination on two of leads F1-F3) to motor 36. A disc-photo-cell combination 42-46 detects that printhead 28 has reached the next print position and applies a signal PC which, with F11, enables 56 to produce signals G2 to enable 24 and BS to initiate production of P1-P35. When the solenoids have been energized, a signal SC resets 52. If, meanwhile, another printable character has been read into 18, flip-flop 50 will have been set: if control 40 receives the resulting F21 signal within 8 msec. of receiving F11 (the first character is printed after more than 8 msec. but less than 15 msec.), another stepping command is transmitted to the motor, causing it to accelerate. The character in 18 is transmitted through 20-26 as before as new bytes are introduced into 18: repeated application of F11, F21 (present simultaneously as both 18, 22 are filled) and PC as each character is printed causes motor 36 to accelerate until stepping takes place at the maximum rate (every 7 msec.) consistent with reliable motor operation. When the last character is being printed only F11 remains: motor 36 thus slows down and then stops. Stepping command signals F1-F3 are derived from a decoder 400, Fig. 4 controlled by signals M1-M3 obtained from a reversible counter 402. This counter is incremented, and motor 36 is stepped to the right, by signals MS1-MS3, derived as follows: MS1: produced once by first character to be printed (signals NCR (v.inf.) and F11); MS2: produced once by first character in 22, second in 18 within 8 msec. (signals OPN, F11, F21); MS3: produced thereafter by each new character to be printed, for stepping at 7 msec. intervals (signals TPN, PC, F21). Counter 402 is decremented when a carriage return signal CR is decoded: CR sets a flip-flop 412 to actuate a ramp generator 410 whose monotonically increasing output causes a UJT relaxation oscillator 406 to produce pulses at an increasing rate so that motor 36 moves print head 28 to the left with minimum delay until a left margin sensor 60 resets 412 by means of a signal OLM, stopping the motor and applying a non-CR signal NCR to buffer 14. This feature is claimed in divided-out Specification 1,403,630. It is stated that provision may also be made for non-printable characters other than carriage return.